This as such is a angle modulated signal, by seeing this we cant differentiate FM and PM, but in more general case we can write angle modulated signal as
s(t)=Acos(ωt +m(t)*h(t))
it is mentioned as a problem in Schuam's sries meant for analog and digital communications..there it is mentioned as "it neither belongs to FM or PM"
i am perplexed...
What is the modulating signal?
The signal
x(t)=A*cos(wt + phi(t))
can be either PM with a modulating phi(t), or FM with modulating d(phi)/dt (the derivative of phi(t)).
Regards